Sullivan County, Missouri · Milan
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Sullivan County averages 45 nights a year at 20°F or colder, mostly November to March, and 44% of its homes predate 1960.
July brings the most downpours to Sullivan County, part of 8.1 heavy-rain days a year. Check the sump first.
Backups often follow heavy rain, which Sullivan County gets about 8.1 days a year, when storm water overloads sewer mains and pushes up through the lowest drain in the house.
In Sullivan County, 4.03 inches fell on the wettest day of the 2015–2024 record. Storms like that, and ice dams in snowy winters, cause most roof leaks.
38% of occupied homes in Sullivan County heat mainly with wood or propane, above the Missouri county median of 24.5%.
About 46 nights a year here stay at 65°F or warmer, so basements and crawl spaces can grow mold even without a leak.
Local risk profile
With 3,010 homes and around 5,857 residents, Sullivan County is 648 square miles of northern Missouri. Besides Milan, the county seat, the biggest communities are Green City, Green Castle and Humphreys. Half the homes here were built before 1965, half after.
59/100 Water Damage Risk Index: Elevated Sullivan County ranks 28 of 114 Missouri counties. See the statewide ranking and method.The three factors where Sullivan County ranks highest compared with other Missouri counties.
Sullivan County gets more hard-freeze nights than most of Missouri. It averaged 117 freezing nights a year over 2015–2024, 45 of them at 20°F or colder, cold enough for pipes in outside walls and crawl spaces to freeze. Among 114 Missouri counties that's 9th.
The longest cold spell was straight 16 days without the temperature rising above freezing, ending in January 2018. The coldest night reached about -16°F on January 15, 2024. Burst pipes usually show up when a spell like that breaks and the ice thaws.
Most freezing nights fall from November to March, peaking in January. Disconnect garden hoses and shut off outdoor spigots before the first hard frost, and keep the heat at 55°F or higher if you'll be away.
Freezing nights typically start around Oct 23 and end around Apr 14.
Sullivan gets fewer downpours than most Missouri counties, but they still fill basements. The county gets about 37.9 inches of rain and melted snow a year, with 8.1 days of an inch or more (106th of 114). Those downpours cluster in June, July and August, when sump pumps and gutters are tested hardest. The wettest day on record brought 4.03 inches on May 29, 2019. The worst three-day stretch dropped 4.78 inches, ending June 27, 2021, the kind of soaking that overwhelms sump pumps and storm sewers.
About 86 days a year swing from below freezing at night to above freezing by day. Those freeze-thaw cycles feed ice dams on roofs, open cracks in foundations and driveways, and stress pipes that are already marginal.
Housing
69% of homes in Sullivan County predate 1980, above the Missouri county median of 53%, which ranks 9th of Missouri's 114 counties.
In Sullivan County 44% of homes are older than 1960. If yours is one of them and the plumbing has never been replaced, expect galvanized steel supply pipe and cast iron drain lines, the two materials most likely to fail quietly.
Manufactured and mobile homes make up 11% of the housing here. Water lines in the underbelly depend on intact skirting and working heat tape, and they're usually the first to freeze in a cold snap.
With 32% of homes empty at survey time, landlords and seasonal owners should shut off the main or schedule checks in winter. An unheated vacant house is also where many policies limit freeze coverage.
Beyond water
Summer nights that don't drop below 65°F, a good marker of humid air, come about 46 times a year here, below the Missouri county median of 64.5. Mold grows when indoor humidity stays above about 60%, the EPA's ceiling. A basement dehumidifier set to 50% and drying anything wet within 24 to 48 hours prevents most problems.
Mold remediation: what to expectBy main heating fuel, Sullivan County homes break down as 29% utility gas, 31% electric, 33% propane and 5% wood. Propane heat is more common here than the state median. Have chimneys swept and fuel-burning appliances serviced each fall, and keep three feet clear around stoves and space heaters.
Fire and smoke cleanup: first stepsCoverage
Calls connect to restoration companies that work across Sullivan County. The largest communities by population:
Population from ACS 2020-2024 5-year estimates. Townships and unincorporated areas are covered too.
Nearby
Mercer and Putnam get more pipe-freeze nights than Sullivan. Linn County has the oldest housing nearby, with 76% of homes built before 1980.
By the numbers
| Factor | Sullivan | Missouri median | Rank |
|---|---|---|---|
| Homes built before 1960 | 44% | 25% | 7 of 114 |
| Homes built before 1980 | 69% | 53% | 9 of 114 |
| Homes built 2000 or later | 13% | 21% | 101 of 114 |
| Manufactured or mobile homes | 11% | 9.8% | 43 of 114 |
| Vacant homes | 32% | 15% | 9 of 114 |
| Wood or propane heat | 38% | 25% | 25 of 114 |
| Nights at 20°F or colder | 45/yr | 28/yr | 9 of 114 |
| Days with 1 inch+ of rain | 8.1/yr | 10/yr | 106 of 114 |
| Freeze-thaw days | 86/yr | 77/yr | 16 of 114 |
| Muggy nights (65°F+) | 46/yr | 65/yr | 102 of 114 |
Rank 1 is the highest value. Bars run from the lowest to the highest Missouri county; the tick marks the median; orange means higher water damage risk than the median, green means lower.
Questions
Peak risk months in Sullivan County: freezing from November to March, heavy rain in June, July and August.
Sources: U.S. Census Bureau, ACS 2024 5-year estimates (2020-2024); weather from NOAA nClimGrid-Daily county averages (EpiNOAA), 2015–2024, averaged across the county; county boundaries from Census TIGER. Reviewed 2026-10-21. Methodology